1. Field of the Invention
The present invention relates to a novel resin composition having superior heat resistance, optical characteristics and mechanical characteristics, a film and optical component comprising the resin composition as well as an image display device and flat panel display utilizing the film.
2. Description of the Related Art
Inorganic glass materials show superior transparency, superior heat resistance and small optical anisotropy, and therefore they are widely used as transparent materials. However, because inorganic glass has a large specific gravity and is brittle, molded grass products have drawbacks that they are heavy, likely to break etc. Due to these drawbacks, development of plastic materials replacing inorganic glass materials is actively done in recent years.
As plastic materials aiming at replacement of such inorganic glass materials, for example, polymethyl methacrylates, polycarbonates, polyethylene terephthalates and so forth are known. Because these plastic materials have a light weight and superior mechanical characteristics and show superior workability, they are recently used for various purposes such as lenses and films.
Further, in the field of flat panel displays such as liquid crystal displays, improvement of damage resistance, lighter weight and smaller thickness have been increasingly needed, and replacement of glass substrates with plastic film substrates is studied. Because plastic film substrates can be flexible substrates, they can be used as substrates of display devices for mobile information communication equipments such as cellular phones and portable information terminals such as electronic notes and laptop personal computers, and therefore plastic film substrates are highly needed.
As heat resistant plastics used for the aforementioned purposes, heat resistant amorphous polymers such as modified polycarbonates (modified PC, see, for example, Japanese Patent Laid-open Publication (Kokai) No. 2000-227603 (claim 7, [0009] to [0019])), polyether sulphones (PES, see, for example, Japanese Patent Laid-open Publication No. 2000-284717 ([0010], [0021] to [0027])) and cycloolefin copolymers (see, for example, Japanese Patent Laid-open Publication No. 2001-150584 ([0027] to [0039])) are known so far.
However, they have a problem that, even if these heat resistant plastics are used, sufficient heat resistance as plastic film substrates cannot be obtained. That is, they have a problem that if a conductive layer is formed on a plastic substrate utilizing any of those heat resistant plastics and then the substrate is exposed to a temperature of 150° C. or higher for providing an oriented film or the like, conductivity and gas barrier property are markedly degraded. Further, for disposition of TFT in the production of active matrix type image display devices, further higher heat resistance is required.
Furthermore, conventional plastic substrates are inferior to glass substrates in optical characteristics. That is, glass has a characteristic that it is optically isotropic in itself. On the other hand, when a plastic material is molded into a film shape, they causes birefringence due to molecular orientation depending on film formation conditions and intrinsic birefringence peculiar to each resin. If a plastic film used for a substrate of display causes birefringence, it causes marked degradation of display quality such as coloration of displayed images and reduction of contrast. Therefore, plastic film substrates are desired to have both of optical isotropy and heat resistance.
As a technique for solving the aforementioned problems of plastic film substrates concerning optical characteristics, for example, Japanese Patent Laid-open Publication (Kokai) No. 2000-227603 mentioned above describes a polycarbonate obtained by copolymerization of 9,9-bis(4-hydroxyphenyl)fluorene (henceforth referred to as “BPFL”) and bisphenol A. This document describes a technique of utilizing BPFL having a negative birefringence to make birefringence as a polymer small. However, the polycarbonate described in the document has a drawback of insufficient heat resistance, although it shows low birefringence. Further, Japanese Patent Laid-open Publication No. 63-314235 (claims) discloses a low birefringence polycarbonate resin utilizing a spiro compound such as spirobiindanediol. However, the polycarbonate resin described in this document has extremely poor mechanical characteristics, and films obtained by molding it are brittle and have problems for practical use.
Further, it is known that heat resistance can be improved by using a bisphenol having a spiro structure such as spirobiindane or a bisphenol having a cardo structure such as fluorene (for example, Japanese Patent Laid-open Publication No. 60-144326 (claims), Japanese Patent Laid-open Publication No. 57-192432 (claim 1, page 8, Example 6, Table) and Japanese Patent Laid-open Publication No. 3-28222 (claim 1)). However, conventional techniques utilize only dicarboxylic acids of common structure (for example, terephthalic acid and isophthalic acid), and the spiro structure or cardo structure can be introduced into a polymer main chain up to only 50 mol % at most.
As described above, any plastic film substrate having high heat resistance and satisfying required performance such as mechanical characteristics and optical characteristics has not been found yet, and it has been strongly desired to solve the problems of the plastic materials proposed so far.